In the paper A. Kryzaniak et al, Extractant screening for liquid-liquid extraction in environmentally benign production routes, Chemical Engineering Transactions, Volume 24, 2011, p. 709-714 is described an extraction process for removing lactic acid from an aqueous solution. The lactic acid concentration in the examples disclosed in the paper was 0.13 M, which corresponds to 1.2% wt. The extractants used were trioctylamine (TOA), N,N,N′,N′-tetramethyl-1,8-naphtalenediamine, N,N-diethyl-m-toluamide, LIX 7950 (LIX 7950 is N,N′-bis(cyclohexyl)-N″-isotridecylguanidine provided by Cognis) and tetradodecyl-bis-N-oxide. According to the paper, the extractant screening resulted in the conclusion that trioctylamine is the most suitable extractant for removing lactic acid from an aqueous solution, wherein lactic acid is present in a concentration of 1.2% wt.
Bacteria in the biomass used in the fermentation process are adversely affected by a decreasing pH, which is proportional to an increasing concentration of free carboxylic acid in the aqueous solution. Therefore there is a need to remove the carboxylic acid even at low concentrations, below 1% wt and suitably at concentrations below 0.5% wt.